The present invention relates to a multi-stage control valve for delivering fuel to a plunger-type high pressure pump for a common rail fuel system.
A common rail fuel delivery system for automotive applications must accommodate three operating conditions: a limp-home or bypass fuel supply condition to provide low-pressure flow from the low-pressure feed pump to the common rail; a zero net flow condition to provide zero flow to the common rail; and a metering condition to provide a metered quantity of flow at high pressure to the common rail.
Commonly, fuel delivery to a common rail fuel pump is implemented by a digitally controlled valve. In this case, the valve default is open, so in the limp-home situation fuel can flow directly from the low-pressure feed circuit through the pumping chamber to the pump discharge valve and on to the common rail. The zero-fueling condition is not a design consideration since the valve is assumed to have zero-leakage for any operating condition; digitally closing the valve achieves zero leakage. Metering is controlled by digitally timing the duration of the opening and closing of the valve.
U.S. Publication No. 2016/0010607 discloses a proportional solenoid operated inlet control valve that is in a normally open condition. In order to achieve the bypass and zero flow conditions, the solenoid must be fully energized, which requires high power consumption. Also, in the bypass condition, that system provides very limited flow in the event of a power failure to solenoid 6 (because the low pressure flow must overcome the opening pressures of check valves 5 and 11). For the zero flow condition, the system of U.S. Publication No. 2016/0010607 relies on the match clearance of bores 27 and 21 and/or the strategy to selectively open valve 5 by the piston 13. Testing has shown that controllability on this condition is inadequate.